This invention relates to a process for the preparation of hydroxyalkylcellulose ethers, more particularly to hydroxyalkylalkylcellulose ethers having C.sub.2 or higher hydroxyalkoxyl functionalities.
Hydroxyalkylcellulose ethers and hydroxyalkylalkylcellulose ethers having C.sub.2 or higher hydroxyalkoxyl functionalities are typically prepared by reacting alkali cellulose with a C.sub.2 or higher alkylene oxide and an etherifying agent which is not an alkylene oxide such as an alkyl chloride, dialkyl sulfate or halocarboxylic acid. In such processes, the alkylene oxide and the etherifying agent are charged into a reaction vessel containing alkali cellulose under reaction conditions, including elevated temperatures, to obtain the desired cellulose ether molecule.
Unfortunately, the alkylene oxide can undergo various side reactions. For example, a molecule of alkylene oxide can react with a molecule of water and a second alkylene oxide molecule to form a glycol ether. The alkylene oxide can also react with the etherifying agent to form ethers therewith. Such side reactions generate impurities which must be removed from the product, and the overall efficiency of the etherification reaction is drastically reduced. For example, in a typical reaction of alkali cellulose with propylene oxide and methyl chloride under conventional conditions, only about 10 to 25 weight percent of the propylene oxide employed reacts with the alkali cellulose as desired.
Recently, in U.S. Pat. No. 4,477,657, a staged continuous addition process for reacting alkylene oxide with alkali cellulose is disclosed. In that process, the efficiency of the alkylene oxide reaction is increased. However, the reaction products can contain high levels of insolubles when preparing hydroxyalkylcellulose ethers and hydroxyalkylalkylcellulose ethers with a high hydroxyalkoxyl substitution, i.e., greater than about 5 weight percent hydroxyalkoxyl substitution.
Accordingly, a process for preparing hydroxyalkylcellulose ethers and mixed hydroxyalkylalkylcellulose ethers with high hydroxyalkoxyl substitution wherein the efficiency of the alkylene oxide reaction is increased and the reaction product has a low level of insolubles would be highly desirable.